This is the last sample format that was only in mpv and not in FFmpeg
(except the spdif special formats). It was a huge pain, even if the
removed code in af_lavrresample is pretty small after all.
Note that this drops S24 from the ao_coreaudio AOs too. I'm not sure
about the impact, but I expect it doesn't matter.
af_fmt_change_bytes() was unused as well, so remove that too.